Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2002-07-24
2004-05-25
Dang, Hung Xuan (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S245000, C359S254000, C385S002000, C385S008000, C385S039000
Reexamination Certificate
active
06741379
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an optical module having an element mounted thereon for shifting an optical phase using the electro-optic effect.
BACKGROUND OF THE INVENTION
Optical communication systems have been introduced to implement large-capacity broadband communication systems. As demands for expanding communication capacity increase, higher bit rate is desired in such optical communication systems.
Meanwhile, in optical communication systems, there has been employed an optical module as an optical modulator, a beam polarizer and an electric shutter, on which an element capable of shifting an optical phase by the electro-optic effect is mounted. Here, the electro-optic effect is a known effect by which a refractive index of a ferroelectric crystal or the like is varied when electric field is applied thereupon.
The element for shifting an optical phase by the electro-optic effect (hereinafter simply referred to as electro-optic effect element) mounted on such an optical module includes an optical waveguide. The optical waveguide is formed by patterning a metal film of Ti, etc. on a wafer being cut from an electro-optic crystal formed of LiNbO
3
, LiTaO
2
, etc. and then by thermal-diffusing or by proton-exchanging in benzoic acid for use in IC manufacturing process. Also, necessary electrodes are produced near the optical waveguide.
The optical module is configured with an optical signal supplied from outside the electro-optic effect element to the optical waveguide and a high frequency control signal of microwave band being supplied to the electrodes produced near the optical waveguide.
FIG. 1
shows a top plan view of a configuration example of the optical module for use in an optical modulator in an uncovered state. An electro-optic effect element
2
is accommodated in a shielding case
1
.
FIG. 2
shows a schematic configuration diagram of electro-optic effect element
2
.
To function as an optical modulator, an optical waveguide
10
formed on electro-optic effect element
2
schematically illustrated in
FIGS. 2A
to
2
C is, as one example, split into a pair of branching waveguides disposed in parallel to form a Mach-Zehnder waveguide.
FIG. 2B
is a cross-sectional view along line ‘a’ in the plan view shown in
FIG. 2A
, while
FIG. 2C
is a cross-sectional view along line ‘b’.
In an exemplary configuration in which a single electrode is employed in the intensity modulation scheme using a Z-cut wafer which is produced by cutting a wafer of electro-optic effect element
2
in Z-axis direction of LiNbO
3
crystal, a signal electrode
20
′ is disposed right on one branching waveguide out of the aforementioned parallel waveguides, while a ground electrode
22
is disposed right on the other branching waveguide. Further, a buffer layer formed of SiO
2
is provided between the wafer and signal electrode
20
and between the wafer and ground electrode
22
, so that an optical signal transmitted in the parallel waveguides is not absorbed in signal electrode
20
and ground electrode
22
.
In
FIG. 2A
, an optical signal is input into the incident side of waveguide
10
(Opt In). To function as an optical modulator, a microwave signal being output from a signal source
25
is supplied to signal electrode
20
as a modulation signal in the same direction as the above-mentioned optical signal transmission direction. Accordingly, a refraction index of the branching parallel optical waveguide varies in mutually opposite direction corresponding to the polarity of the microwave signal. This produces an optical phase difference in each parallel optical waveguide, to output an optical signal being intensity-modulated from an output side (Opt Out) of optical waveguide
10
shown in FIG.
2
A.
Here, in the optical module configuration shown in
FIG. 1
, a high frequency signal i.e. a microwave modulation signal fed from signal source
25
is supplied between signal electrode
20
and ground electrodes
21
,
22
through an RF connector
3
consisting of a center conductor
30
and an outer conductor
31
.
At this time, in the conventional configuration shown in
FIG. 1
, center conductor
30
of RF connector
3
is inserted into a sliding contact member
32
to connect with signal electrode
20
of electro-optic effect element
2
by bonding. Also, in this conventional configuration, outer conductor
31
of RF connector
3
is connected to ground electrodes
21
,
22
of electro-optic effect element
2
through a bonding wire
23
.
However, a sufficient space for inserting a bonding tool was required for this bonding. For this reason, it was inevitable to protrude center conductor
30
of RF connector
3
from the coaxial condition of RF connector
3
. This causes increased characteristic impedance in the protrusion portion of center conductor
30
in RF connector
3
, resulting in producing impedance mismatch.
Further, though the characteristic is not influenced so much when the wavelength of a high frequency signal is long as compared to the size of the electrode in electro-optic effect element
2
, the high frequency characteristic of electro-optic effect element
2
is substantially influenced when the high frequency signal wavelength becomes shorter. As a result radiation and reflection are produced in the high frequency signal, and a wideband transmission characteristic in electro-optic effect element
2
becomes impeded. Also, the sizes of slide contact member
32
and center conductor
30
of RF connector
3
are as minute as several tens &mgr;m. Therefore, efficiency in assembly work is significantly bad.
To cope with these problems, the inventors of the present invention have been studying of adopting a method of using an intermediate or repeating board (hereinafter, called as repeating board). However, in the connection between RF connector
3
and electro-optic effect element
2
through the repeating board, even when designing a characteristic impedance to be, for example, 50 &OHgr; in each portion itself, it is inevitable to have an abrupt impedance variation in the connection of RF connector
3
and the repeating board. As a result, still there has been a problem of an increased transmission loss.
SUMMARY OF THE INVENTION
Accordingly, in an optical module on which an element for shifting an optical phase by the electro-optic effect is mounted, it is an object of the present invention to provide a preferable configuration of the optical module to circumvent a loss produced when a high frequency control signal is externally supplied through an RF connector.
According to the present invention to solve the aforementioned problem, as a first embodiment of the optical module having an element for shifting an optical phase by the electro-optic effect, the optical module includes; the element for shifting an optical phase by the electro-optic effect having a signal electrode and a ground electrode formed thereupon; a connector for supplying a control signal of a microwave region to the signal electrode of the element, having a center conductor and an outer conductor; and a repeating board formed on a dielectric wafer having the signal electrode and the ground electrode of the element and a coplanar line for connecting the center conductor of the connector with the outer conductor respectively formed on the dielectric wafer. Here, an air layer is formed on the lower portion of the repeating board on which the center conductor of the connector is disposed.
As a second embodiment of the optical module to solve the aforementioned problem, in the first embodiment, the air layer is formed on the lower portion of the repeating board on which the center conductor of the connector is disposed is formed by a notch produced on the side face of the dielectric wafer positioned oppositely to the connector.
As a third embodiment of the optical module to solve the aforementioned problem, in the second embodiment, the coplanar line is constituted by a signal electrode and ground electrodes disposed on both sides of the signal electrode. The interval between t
Ishizaka Tetsuo
Kaitoh Yoshihiko
Tanaka Takehito
Dang Hung Xuan
Fujitsu Limited
Staas & Halsey , LLP
Tra Tuyen
LandOfFree
Optical module having element for optical phase shift using... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical module having element for optical phase shift using..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical module having element for optical phase shift using... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3249284